Ultra-high-frequency signaltranslating stage



April 14, 1942. H. A. WHEELER 2,279,543

ULTRA-HIGH-FREQUENCY SIGNAL TRANSLATING STAGE Original Filed Oct. 29, 1938 FIGJ.

7 4E MW INVENTOR 4 Y H OLD A. WHEELER ATTORN EY Patented Apr. 14,

- ouraa-nrcn-rnnquancr SIGNAL- 'raansm'rmc s'rsca Harold A. Wheeler, Great Neck, N. Y., assignor to Hazeltine Corporation, a corporation of Dell.-

. ware Original application October 29, 1938, Serial No.

1939, Serial No. 277,862

14 Claims.

This invention relates generally to ultra-highfrequency signal-translating stages for operation at such high frequencies that the conductance of the input circuit of the stage is an appreciable factor in determining the response characteristic of the stage.

This application is a division of applicant's copending application, Serial No. 237,665, entitled Tunable selector of uniform band width." filed October 29, 1938, now United States Patent No. 2,196,881, issued April 9, 1940.

The input conductance of conventional vacuum tubes utilized in ultra-high-frequency translating stages, such as ultra-high-frequency amplifiels, tends materially to reduce the response of the stage. At frequencies above megacycles or thereabout, the input conductance of conventional vacuum tubes is appreciable, while at frequencies higher than 50 megacycles, the input conductance, rather than the inherent tube and circuit capacitance, becomes a limiting factor in the response of the stage. The reason for this condition is that the maximum impedance which can be developed across the input circuit of the stage at such ultra-high frequencies is limited by the input conductance of the tube.

I Also, at ultra-high frequencies, the input capacitance of such a stage and the variation of input capacitance with variations of the transconductance of the vacuum tube utilized are both appreciable, thereby adding other limitations to the response characteristic of the system. While there have'been proposed arrangements for reducing the input capacitance of a vacuum tube and for maintaining it substantially uniform with variations of the transconductance of the tube. when utilized in such an ultra-high-frequency stage, such arrangements in themselves have not been efiective tocompensate for the conductance of the input circuit and some arrangements for stabilizing the input capacitance have even introduced appreciable additional conductance into the input circuit. It is, therefore. desirable to provide an arrangement which may be used in such systems for maintaining relatively constant input capacitance and which is efiective to reduce too. low value the conductance of the input circuit of the stage.

It is an object of the present invention, therefore, to provide an improved ultra-high-frequency signal-translating stage which is not subject to the above-mentioned disadvantages of the arrangements of the prior art. K g

It is a further object of the invention to provide an improved ultra-high-frequency signal- Divided and this application June 7,

translating stage, the response of which is not substantially limited by the conductance of the input circuit of the vacuum tube included in the stage.

In accordance with the invention, an ultrahigh-frequency signal-translating stage for operating over a wide band of frequencies comprises,

a vacuum tube having a cathode, an anode, and

a control electrode, an input circuit coupled to the cathode and the control electrode and tunable over the aforesaid band of frequencies, and an output circuit coupled'to the anode and the cathode. The stage has incidental reaction to the input circuit tending to develop substantial positive conductance thereacross under normal operating conditions of the stage. The stage also includes an additional electrode in the vacuum tube between the control electrode and the anode, the stagehaving appreciable capacitance between the control electrode and the additional electrode, and means for minimizing the feedback from the output circuit to the input'circuit of signal energy of the frequency to which the input circuit is tuned. There is also included in the signal-translating stage a circuit coupled to the additional electrode and the cathode including an inductance proportioned to render the additional electrode circuit inductively reactive over the band of operating frequencies of the input circuit,.and means for applying a unidirectional positive potential to the additional electrode, the inductance being of such value with respect to the aforesaid capacitance as effective- 1y to neutralize a substantial part ofthe aforesaid conductance of the'input circuit over the aforesaid band of? operating frequencies.

The novel features which are believed to be characteristic of the invention are set forth with particularity in the appended claims. The invention itself, however, both as to its organiza-' tion and method of operation, together with other and further advantages thereof, will best be understood with reference to the following specification, taken in connection with the accompanying drawing in which Fig. l is a circuit diagram of a stage of ultra-high-freq'uency amplification incorporating the invention; and Fig. 2 is another embodiment of the invention comprising a modification of the circuit of Fig. 1-

The input conductance of conventional vac uum tubes comprises three components: (1) that due to the dielectric loss of the tube insulators and they tube base and the e'flect of the space charge in the region of the cathode; (2) that due to reaction from the anode-cathode circuit to the grid-cathode circuit through the gridcathode capacitance of the tube and the selfinductance of the cathode lead, the latter being common to the input and output circuits; and (3) that due to reaction caused by the finite transit time of electrons through the tube. The component of input conductance (1) is usually small as compared with that due to feedback through the grid-cathode capacitance and the self-inductance of the cathode lead, and also is small as compared to that component of the input conductance dependent on the transit time of electrons through the tube. A

The magnitude of the component of input conductance of a conventional vacuum tube due to T the transit time of electrons through the tube has been derived mathematically by D. 0. North (see Proceedings of the Institute of Radio Engineers, vol. 24, No. 1, January 1936, page 108 et seq). A mechanical explanation of the effect of transit time of electrons on the input conductance of a vacuum tube has been developedby W. R. Ferris (see Proceedings of the Institute of Radio Engineers, vol. 24, No. 1, January 1936, page 82 et seq). These authors have shown that the component of input conductance Gt of conventional vacuum tubes dependent on the transit time of electrons throughthe tube is:

Gr==F gm (1) where:

F is a function of the transit time;

(u is the mean angular frequency of .the signal translated by the stage; and

gm is the transconductanceof the tube.

' The factor F is dependent only slightly on varia- Le is the inductance of the cathode lead common to both the input and output circuits of the tube.

The total input conductance due to reaction to the input. circuit of such a high-frequency stage,

neglecting that component due to dielectric losses, may, therefore, be expressed as:

where L'c is a simulated cathode-lead inductance that would account for the total input conductance of the tube solely on the basis of feedback through the grid-cathode capacitance. It will be seen from Equation 3 that the positive conductance of the input circuit increases with frequency over the operating frequency range of the stage. The simulated cathode-lead conductance as determined from Equation 3 has the value:

= w C gm (4) Such an ultra-high-frequency stage of amplification is shown in the circuit of Fig. 1 in which reference numerals correspond to those identifying the same circuit elements in the above-mentioned copending application. This ultra-highfrequency signal-translating stage is adapted to operate overa wide band of frequencies and comprises a vacuum-tube amplifier H having an input circuit including an adjustable inductor 3| tuned by capacitance 36, shown in dotted lines for the reason that it may be comprised in whole or in part of the inherent capacitance of the circuit of the control electrode or grid of tube H, coupled to the control grid and .cathode of tube H and tunable over'the operating band of frequencies. A grid-leak resistor 38 is provided for tube ll, by-passed for high-frequency currents by a condenser 31. The output circuit of the stage includes a tuned circuit comprising a condenser l4 and an inductance I5 coupled to the anodeand cathode of tube II. The amplifier stage thus far described has incidental reaction to the input circuit 3|, 36 tending to develop substantial positive conductance .thereacross under normal operating conditions. In accordance with'the invention, an additional electrode I6 is provided in vacuum tube H between the control grid and the anode of the tube. The amplifier stage includes a circuit coupled to the additional electrode I 6 and the cathode including elements of fixed values providing inductive reactance which increases with frequency over the operating frequency band of the stage comprising an inductance 42 proportioned to render the additional electrode circuit inductively reactive over the band of operating frequencies of the input circuit 3|, 36. There is also provided means for applying a unidirectional positive potential to the additional electrode l6 comprising. a unidirectional source ll included in series with the inductance 42 in the additional electrodecathode circuit. Acapacitance 44 is efiectively coupled between the control grid of tube II and the additional electrode l6 and is shown in dotted lines for the'reason that it may be comprised in whole or in part of interelectrode capacitance within the tube.

In considering the operation of the circuit of Fig. 1, it will be seen that negative conductance is introduced into the input circuit of the highfrequency stage shown, due to the voltage developed across inductance 42 and fed back to the input circuit through capacitance 44. This-negative conductance -G varies in accordance with.

In accordance with the invention, therefore, the positive conductance of the input circuit represented by Equation 3 is wholly or partially neutralized by the negative-conductance effect of.

the added inductance 42, as given by expression (5). In order to produce exact neutralization, the positive conductance 'of Equation 3 is made to be equal to thenegative conductance of expression (5). That is:

Therefore, it is seen that the invention may be utilized simply by connecting an inductance In in the screen-grid circuit of a. conventional vacuum tube, the value of inductance being de- From Equation 7 it willbe seen that the inductance L. is so proportioned with respect to the simulated inductance L'c that the voltage developed across the inductance LB and coupled tothe input circuit 3|, 36 through the capacitance M eflectively neutralizes a substantial part of the positive conductance in the input circuit over the band of operating frequencies. In practice, however, it may be more convenient to place an adjustable inductance in the circuit in place of inductance 42 in order that its inductance may be adjusted to determine the exact inductance required for neutralization. v

In the foregoing described operation of the Fig. 1 embodiment of the invention, the feedback conductance component in the input circuit, which is produced by the feed-back through the anode-to-control-grid capacitance of tube H the tuned output of the signal developed across circuit l4, l5 has been ignored on the assumption that this component of conductance is negligible in comparison to that produced by t e auxiliary electrode 16. This analysis and assumption is correct where the output circuit l4, I5 is tuned to an operating frequency considerably difierent from that of the input tuned circuit 3|, 36, as in the arrangement of Fig. 9 of the aforementioned Wheeler patent where the output circuit of the amplifier H is .tuned to a relatively low intermediate frequency and the input circuit is tuned to the relatively high frequency of a received carrier signal. In this event, the output tuned circuit [4, I5 of the present arrangement-has relatively low impedance at the frequency of the input signal and consequently little or no signal voltage of this .frequency is developed across the output circuit and is fed back to ode-to-control-grid capacitance. Consequently, thecomponent of conductance due to the anodetermined in accordance with Equation '1 above.

However, it will be auxiliary electrode frequencies so that fills theusual function of a screen-grid electrode in a vacuum tube. For this reason, it may be desirable to include an additional electrode, which has the usual functions of a screen grid. between the auxiliary electrode it and the anode of vacuum tube l I. This arrangement is shown in Fig.- 2 in which the additional screen electrode It varies somewhat atsignal is represented at l8. The circuit of Fig. 2 is otherwise identical to that of Fig. 1- and it is believed that the operation of the circuit of Fig. 2 will be readily understood from the description given'above with reference to the operation of Fig. 1. Y

From theabove description of the invention, it will be seen that the inductance 42 is of such value with respect to the capacitance 44 between the additional electrode 15 and the control grid of tube I! as eifectively to neutralize a substantial part of the positive conductance of the input the control grid through the anto-control-grid capacitance is negligible and may be ignored. This is also true in the case where the output tuned circuit l4, i5 is tuned to the same operating frequency as the input tuned circuit 3|, 3B, but is heavily damped as required in a wide-band amplifier. I

Where it is necessary that the output tuned circuit l4, l5 be resonant with the input tuned circuit 31, 36 at the same operating frequency and have high selectivity, an appreciable signal voltage is then developed across the output tuned circuit. The component of the conductance due to the feedback of this voltage through the anode-to-control-grid capacitance detrimentally affects the desired balance of positive and negative conductances over the wide range of operating frequencies of the stage unless the effective anode-to-control-grid capacitance is reduced to a small value by interelectrode shielding means. In accordance with one feature of the invention, therefore, the detrimental efiect of an appreciable value of anode-to-control-grid capacitance, which would tend to impair the desired operation if the input and output circuits of the amplifier were tuned together to any given operating frequency in the wide frequency band, is reduced by the provision in tube ll of certain electrodes, for example, a suppressor grid as shown in the Fig. l arrangement, and the suppressor and screen grids of Fig. 2 presently to be considered.

The suppressor grid of the circuit of Fig. 1 also greatly reduces the coupling between the auxiliary electrode I6 and the output anode.

circuit 3|, 36 over theband of operating frequencies.

While there have been described what are at present considered to .-be the preferred embodiments of this invention, it will be obvious to those skilled in the art that various changes and modifications may-be made therein without departing from the invention, and it is, therefore, aimed in the appendedclaims to cover all such changes and modifications as fall within the true spirit and scope of the invention.

What is claimed is:

1. An ultrahigh-frequency signal-translating stage for operating over a wide band of frequencies comprising, a vacuum tube having a cathode,

an anode, and a control electrode, an input circuit coupled to said cathode and said control electrode and tunable over said band of frequencies, an output circuit coupled to said anode and said cathode, said stage having incidental reaction to said input circuit tending to develop substantial positive conductancethereacross under normal operating conditions, an additional electrode in said vacuum tube between said control electrode and said anode, said stage having appreciable capacitance between said control electrode and said,additional electrode, means for minimizing the feedback from said output circuit to said input circuit of signal energy of the frequency to which said inputcircuit is tuned, a circuit coupled to said additional electrode and said cathode including inductance proportioned to render said additional electrode circuit inductively reactive over .said range of operating frequencies of said input circuit, and means for applying a unidirectional positive potential .to said additional electrode, said inductance being of such value with respect to said capacitance as effectively to neutralize a substantial part of said conductance of said input circuit over said band of operating frequencies.

2. An ultra-high-frequency signal-translating additional electrode in said vacuum tube between seen that the potential 0! it no longer completely fulsaid control electrode and said anode, said stage having appreciable capacitance consisting of only interelectrode capacitance between said control electrode and said additional electrode, means for minimizing the feedback from said output circuit to said input circuit of signal energy of the frequency to which said input circuit is tuned, a circuit coupled to said additional electrode and said cathode and including inductance proportioned to render said additional electrode circuit inductively reactive over said range of operating frequencies of said input circuit, and means for applying a unidirectional positive potential to said auxiliary electrode, said inductance being of such value with respect to said capacitance as effectively to neutralize a substantial part of said conductance of said input circuit over said band of operating frequencies. Y

3. An ultra-high-frequency signal-translating stagefor operating over a wide band of frequencies, comprising, a vacuum tube having a cathode, an anode, and a control electrode, an input tuned circuit coupled to said cathode and said control electrode and tunable over said band of frequencies, an output tuned circuit coupled to said anode and said cathode, said stage having incidental reaction to said input circuit tending to develop substantial positive conductance thereacross under normal operating conditions of said stage, an additional electrode in said vacuum tube between said control electrode and said I anode, said stage having appreciable capacitance between said control elect ode and said additional electrode, means for miiilmizing the feedback from said output circuit to said input circuit of. signal energy of the frequency to which said input circuit is tuned, a circuit coupled to said additional electrode and said cathode and including inductance proportioned to render said additional electrode circuit inductively reactive over said range of operating frequencies of said input circuit, and means for applying a unidirectional positive potential to said auxiliary electrode, said inductance being of such value with respect to said capacitance as effectively to neutralize a substantial part of said conductance of said input circuit over said band of operating frequencies.

4. An ultra-high-frequency signal-translating stage for operating over a wide band of frequencies comprising, a vacuum tube having a cathode,-an anode, and a control electrode, an input circuit coupled to said cathode and said control electrode and tunable over said band of frequencies, an output circuit coupled to said anode and said cathode, said stage having incidental reaction to said input circuit tending to develop substantial positive conductance thereacross under normal operating conditions of said stage,-an additional electrode in said vacuum tube between said control electrode and said anode, said stage having appreciable capacitance between said control electrode and said additional electrode, a circuit coupled to said addional electrode and said cathode and including inductance proportioned to render said additional electrode circuit inductively reactive over said range'of operating frequencies of said input circuit, a screen electrode between said additional electrode and said anode for minimizing the feedback from said output" circuit to said input circuit of signal energy of the frequency to which said input circuit; 'is tuned',fand means for applying a unidirectional positive potential to said additional electrode,- saidf inductance be- I aa'ramt ing of such value with respect to said capacitance as to neutralize a substantial part of said conductance of said input circuit over said band of operating frequencies. v 1

5. An ultra-high-frequency signal-translating stage for operating over a wide band of frequencies comprising, a vacuum tube having a cathode, an anode, and a control electrode, an input-circuit coupl to said-cathode and said control electrode and tunable over said band of frequencies, an output circuit coupled to said anode and said cathode, said stage having incidental reaction to said input circuit tending to develop substantial positive conductance thereacross under normal operating conditions of said stage, an additional electrode in said vacuum tube between said control electrode and said anode, said between said control electrode and said additional electrode, asuppressor electrode between said additional electrode and said anode for the feedback from said output circuit to said input circuit of signal energy of the frequency to which said input circuit is tuned, a circuit coupled to said additional electrode and said cathode and including inductance proportioned to render said additional electrode circuit inductively'reactive over said range of operating frequencies of said input circuit, and means for applying a positive potential to said additional electrode, said inductance with respect to said capacitance as to neutralize a substantial part of said conductance of said input circuit over said band of operating frequencies. g 6. An ultra-high-frequency signal-translating stage for operating over a wide band of frequencies comprising, a .vacuum tube having a,

cathode, an anode, and a control electrode, an

input circuit coupled to said cathode and said control electrode and and output circuits, an additional electrode in said vacuum tube between said control electrode additional electrode, said additional electrode circuit inductance being so proportioned with respect to said simulated inductance that the voltage developed across said additional electrode circuit inductance and coupled to said input circuit through said capacitance effectively neutralizes a substantial part of said conductance in said input frequencies.

7. An ultra-high-frequency signal-translating stage comprising, a vacuum tube having a cathcircuit over said band of operatingode, an anode, and a control electrode, an input being of such value input circuit is tuned, a circuit circuit coupled to said cathode and said control electrode, an output circuit coupled to said anode and said cathode, said stage comprising incidental reaction to said input circuit tending to develop substantial positive conductance Gg thereacross under normal operating conditions of said stage, an additional electrode'in' said vacuum tube between said control electrode and said anode, said stagehaving appreciable capacitance Cgs between said control electrode and said additional electrode, a circuit coupled to said additional electrode and said cathode and including inductance having a value Ll proportioned to render said additional electrode circuit inductively reactive at the operating frequency of said stage, and means for applying a unidirectional. positive potential to said additional elec trode, said inductance and capacitance being proportioned in accordance with the expression Gg: gmw c'gsLr where w is the mean frequency of the signal input to said stage and gm the value of transconductance between said control electrode and said additional electrode.

8. An ultra-high-frequency signal-translating stage comprising, a vacuum tube having a cathode, an anode, and a control electrode an input circuit coupled to said cathode and said, control electrode, an output circuit coupled to said anode and said cathode, said stage comprising an interelectrode capacitance Cgo between said control electrode and said cathode and having an incidental reaction to said input circuit tending to develop substantial positive conductance G; thereacross under normal operating additional electrode and said cathode including inductance proportioned to render said additicnal electrode circuit inductively reactiveover said range of operating frequencies of saidinput circuit, and means for applying a unidirectional positive potential to said additional electrode, said inductance being of such value with respect to said capacitance as effectively to neutralize a substantial part ofsaid conductance of said input circuit over said band of operating frew quencies. t

10. An ultra-high-frequency signal-translating stage for operating over a wide band of frequencies comprising, a vacuum tube having a cathode, an anode, and a control electrode, an input 'circuit coupled to said cathode and said control electrode and tunable over said band of frequencies, an output circuit coupled to said anode and said cathode and including a portion common to said input circuit, said stage having incidental reaction to said input circuit tending to develop substantial positive conductance thereacross .under normal operating conditions of said stage which is effectively simulated by an inductance in said common portion of said input and' output circuits, an additional electrode-in said vacuum tube, said control electrode having positive transconductance with respect to said, additional electrode, said stage having appreciable capacitance between said control electrode and said additional electrode, means for minimizing the feedback from said output circuit to said input circuit of signal energy of conditions of said stage, an additional electrodea in said vacuum tube between said control electrode and said anode, said stage having appreciable capacitance C 5 between said control electrode and said additional electrode, a circuit coupled to said additional electrode and said cathode and including inductance having a value Ls proportioned to render said additional electrode circuit inductively reactiveat the operating frequency of said stage, and means for applying a positive unidirectional potential to said additional electrode, said inductance and capacitance being proportioned in accordancewith the expression.

where the parameters have the significance given in the specification.

9. An ultra-high-frequency signal-translating stage for operating over a wide band -of frequencies comprising, a vacuum tube having a cathode, an anode, and a control electrode, an input circuit coupled to said cathode and said control electrode and tunable over said band of frequencies, an output circuit coupled to said anode and said cathode, said stage having incidental.reaction to said input circuit tending to develop substantial positive conductance thereacross under normal operating conditions, an additional electrode in said vacuum tube, said control electrode having positive transconductance with respect to said additional electrode, said stage having appreciable capacitance between said controlelectrode and said additional electrode, means for minimizing the feedback from said output circuit to said input circuit of signal energy of the frequency to which said input circuit is tuned, a circuit coupled to said the frequency to which said input circuit is tuned, a circuit coupled to said additional electrode and said cathode, and? including inductance proportioned to render said additional electrode, circuit inductively reactive'over said range of operating frequencies of said input circuit, and means for applying a unidirectional positive potential to said additional electrode, said additional electrode circuit inductance being so proportioned with respect to said simulated inductance that the voltage developed across said additional electrode circuit inductance and coupled to said input circuit through said capacitance effectively neutralizes a substantial part of said conduc- I tance in said input circuit over said band of op erating frequencies. a

11. An ultra-high-frequency signal-translating stage comprising, a vacuum tube having a cathode,,an anode, and a control electrode, an input circuit coupled to said cathode and said control electrode, an output circuit coupled to said anode and said cathode, said stage comprising incidental reaction to said input circuit tendingto develop substantial positive conductance Gg thereacross under normal operating conditions of said stage, an additional electrode in said vacuum tube, said control electrode having positive transconductance with respect to said additional electrode, said stage having appreciable capacitance Cgs between said'control electrode and said additional electrode, a circuit coupled to said additional electrode and said cathode and including inductance having a value Ls proportioned to render said additional elec trode circuit inductively reactive at the operating frequency of said stage, and means for apwhere w is the mean frequency of the signal input to said stage and gm the value of transa cathode, an anode, and a control electrode, an

input circuit coupled to said cathode and said control electrode, an output circuit coupled to said anode and, said cathode, said stage comprising an interelectrode capacitance Cgc between said control electrode and said cathode and having an incidental reaction to said input circuit tending to develop substantial positive conductance G; thereacross under normal operating conditions of said stage, an additional electrode in said vacuum tube, said control electrode having positive transconductance with respect to said additional electrode, said stage having appreciable capacitance C between said control electrode and said additional electrode, a circuit coupled to said additional electrode and said cathode and including inductance having a value L, proportioned to render said additional electrode circuit inductively reactive at the operating frequency of said stage, and means for applying a positive unidirectional potential to said additional electrode, said inductance and capacitance being proportioned in accordance with the expression l Y L Q u C gm where the parameters have the significance given in the specification.

13. An ultra-high-frequency signal-translating stage for operating over a wide band of frequencies comprising, a vacuum tube having a cathode, an anode, and a control electrode, an input circuit coupled to said cathode and said control electrode, an output circuit coupled to said anode and said cathode, said stage having incidental reaction to said input circuit tending to develop thereacross substantial positive c0n ductance which increases with frequency over the operating range of said stage, an additional electrode in said vacuum tube, said control electrode having positive transconductance and appreciable capacitance with respect to said additional electrode, a circuit included between said additional electrode and said cathode comprising elements of fixed values providing inductive reactance which increases with frequency over said operating frequency range, said inductive reactance being of such value with respect to said capacitance as eifectively to neutralize a substantial part of said c nductance over said operating range.

14. An ultra-high-frequency signal-translating stage for operating over a wide band of frequencies comprising, a vacuum tube having a cathode, an anode, and a control electrode, an input circuit coupled to said anode and said cathode and including a portion common to said input circuit, said stage having incidental reaction to said input circuit tending to develop thereacross substantial positive conductance which increases with frequency over the operating range of said stage and which is eifectively simulated by an inductance in said common portion of said input and output circuits, an additional electrode in said vacuum tube, said control electrode having positive transconductance and appreciable capacitance with respect to said additional electrode, a circuit included between said additional electrode and said cathode comprising elements of fixed values providing inductive reactance which increases with frequency over said range, said inductive reactance being so proportioned with respect to said simulated inductance that the.vo1tage across said elements and coupled to said input circuit through said capacitance efiectively neutralizes a substantial part of said conductance in said input circuit over said operating range.

- HAROLD A. WHEELER. 

